1. Field of the Invention
This invention relates to a method and an apparatus for producing a rapidly solidified metallic tape, and more particularly to an improvement in the shape, particularly side edge shape of the metallic tape obtained through twin-roll process while stably maintaining continuous operation.
2. Related Art Statement
As a production method of the metallic tape, the twin-roll process as shown in FIG. 2 is developed and put into practical use. In the twin-roll process, molten metal 1 is continuously supplied from a pouring nozzle 2 to a kissing region between a pair of cooling rolls 3, 3 rotating at a higher speed to form a rapidly solidified metallic tape 4.
However, the metallic tape produced by the twin-roll process generally has a crown shape, wherein the central portion is thick and both side edge portions are thin. Further, the saw-tooth shape or the oxidized area is formed in both the side edge portions. In order to obtain a sound product, therefore, it is obliged to cut away both the side edge portions from the resulting tape, resulting in the reduction of yield.
This is considered due to the fact that excessive molten metal periodically flows in the axial direction of the roll owing to the unbalance between pouring rate and solidification rate and the molten metal height is lower at the vicinity of both side edge portions of the roll than at the central portion thereof, and consequently heat crown is caused to produce solidification cracks in both side edge portions of the tape and the break-out is caused or the oxidized area is formed.
In order to solve these problems, therefore, there have hitherto been proposed many methods for holding molten metal at the kissing region between rolls. Among these methods, there is a typical method as shown in FIGS. 3a and 3b, wherein molten metal 1 is poured into a space defined by two cooling rolls 3, 3 and two fixed stoppers (side plates) 5 pushed to the side faces of the rolls to continuously produce a metallic tape 4. In the latter method, however, molten metal is cooled by atmosphere or by the side plates, so that the adhesion of solidified or semi-solidified shell to the side plate increases, and finally such a shell falls off from the side plate into the space between rolls and is entrapped in the cast tape to produce discontinuous part therein, which causes operation troubles such as tape cutting, roll stop or roll deformation based on the occurrence of abnormal reaction force to the reduction, and the like.
In Japanese patent laid open No. 57-130,743 is proposed a method, wherein an end keep 5 provided with a porous refractory 6 is pushed to the side edge of the roll 3 to thereby prevent the leakage of molten metal 1 and at the same time an inert gas 7 is supplied through the porous refractory 6 to prevent the formation of solidification shell based on the cooling of molten metal as shown in FIG. 4. In this method, however, it is very difficult to uniformly supply the inert gas over the whole of the side edge face of the roll, so that the formation and adhesion of solidification shell to the side edge face of the roll can not completely be prevented. For this end, once the solidification shell is adhered to the side edge face, the growth of the shell can not be prevented by this method. As a result, the abrading is promoted by the long-period use to cause the thrusting of molten metal into the resulting gap between the side edge face of the roll and the end keep, so that the continuous pouring is still impossible.
In Japanese patent laid open No. 60-234,744 is proposed an apparatus wherein the end keep is replaced with a caterpillar- or belt-type movable side seal 8 and a fixed side plate 5 is pushed to the movable side seal 8 for improving the adhesion property to the side edge face of the cooling roll 3 as shown in FIGS. 5a and 5b.
In this apparatus, the metallic tape is produced by moving the movable side seal in the same direction as the pouring direction of molten metal or the travelling direction of the tape to reduce the adhesion of solidification product to the side seal.
Although the leakage of molten metal from the side edge face of the roll is fairly prevented in the above apparatus, if the solidification product is slightly formed on the side seal, it is squeezed between the rolls to form a gripped portion in the cast tape at the kissing region. Particularly, in case of tapes having a thinner thickness, the above gripped portion largely affects the properties of the side edge portion of the tape, resulting in the occurrence of break-out.
In Japanese patent laid open No. 58-212,845 is proposed an apparatus for preventing the break-out of the tape, wherein a part of the side plate is replaced with a movable water-cooled roll 9 to produce the solidification product in the side edge portion of the roll as shown in FIGS. 6a and 6b. In this apparatus, however, there are caused the same problems as in the aforementioned Japanese patent laid open No. 60-234,744.
In any case, the adhesion of solidification product to the side plate can not be avoided according to the conventional techniques, so that the properties of the side edge face of the tape are apt to be degraded and the break-out is apt to be caused, and hence the continuous pouring becomes difficult industrially.